The present invention relates to novel cephalosporin analogs and more specifically to new carbacephem compounds which differ from cephalosporin by having carbon atom instead of sulphur atom in dihydrothiazine ring. In the Journal of the American Chemical Society, 96, 7584 (1974) and J. Med. Chem., 20, 551 (177) certain carbacephems with substituted methyl groups at the C-3 position such as (.+-.)-1-carbacephalotin represented by the formula: ##STR1## are disclosed as having antibacterial activity. Nevertheless as microorganism populations develop immunity to existing antibiotics new antibacterial compounds are in demand. To this end, as is disclosed hereinafter, novel carbacephems with hydrogen atom at C-3 position have been synthesized which are useful as intermediates in the preparation of unexpectedly high antibacterial compounds.